Speedometer correction

[reallyflyguy]

Hey!

I'm changing my final drive from the stock 3.29 to 3.55

Is there any possibility of correcting the speedometer?

[Spunkster]

Only for the dash in the sensors section of the calibration window.

[AWOC]

I got one of these. Works great! https://www.brockwayengineering.com/pdf ... Manual.pdf

It would be great if Hondata can make this a quick drop down selection for fixing this. Is there a way, or impossible Hondata?

[Ayesuh]

Ive looked, no option for speedometer calibration input on 07-08 TL flashpro..... am i missing something because i also would like to get the dash to read proper :/

[Ayesuh]

Errrrr.... so heres some info for yall at hondata..... maybe with this info, we can get a speedometer calibration on the Flashpro TL.....

When asking about the SC100 (plug and play for Final Drive)

Quoted text below:
The speed input to the ECU comes from a sensor that reads the number of pulses generated by the teeth of 3rd gear.
And this is the gear that resides on the countershaft. The ECU program has a scaling factor that is set for the number
of pulses expected in one kilometer (or mile). So, if the FD gears are changed, or the number of teeth on 3rd gear, then
the calibration will be wrong and the CAN message that gets sent to the instrument cluster will have the wrong value.

Ideally, you would just tweak the scaling factor in the ECU. Hondata offers this feature for other applications, but never
included it in the V6 versions of FlashPro. At least not to our knowledge. K-Tuner is supposedly working on adding
this feature, but we aren't sure when it will be implemented.

[keltalon]

I recently purchased a 3.55 gear from p2r, and I noticed my speedometer is reading 8% off. I’ve been searching for a solution for over a week but haven’t found anything viable. Could Hondata kindly consider adding a speed calibration feature, similar to what other tuning platforms offer? This would be incredibly helpful for users like me. Thank you!

[Ayesuh]

I already talked with hondata.... they didnt say why but they said it wasnt possible..... i contacted 'yellow box' about their speed signal adjuster, they have a plug and play solution.... although wont have an exact ratio conversion for my purpose.... hoping its close enough for me, but give them a try

[Ayesuh]

Yellr is the website for the yellow box..... sorry for leaving that part out!

[keltalon]

I recently installed a plug-and-play yellow box, and now my speedometer matches perfectly with the GPS reading. However, I noticed that VTEC started engaging at 3600 RPM. I attempted to adjust the engagement point in Hondata but had no success. To resolve the issue, I split the sensor signal, and everything works perfectly now. I ran a wire from pin #10 of the ECU to the blue wire before it enters the yellow box sensor. This setup ensures the ECU receives the 3.55 gear speed reading, while the modified yellow box flawlessly sends the correct signal to the dash!

[keltalon]

Here's an update: I was still experiencing issues with the Yellow Box. While it corrected my speedometer, it caused problems when set to around a 10% alteration. Specifically, it disrupted my VTEC, making it engage at 3600 RPM regardless of the settings in FlashPro. Additionally, my ECU struggled to determine which gear I was in. However, for anyone using the Yellow Box, here's the fix.

Let’s re-sketch the whole chain including the TL ECU’s B9 pin and your Yellow-Box, so you can see exactly where everything plugs in:

pgsql
Copy
Edit
Transmission
VSS Sensor
│
G/W ──┴──► ECU “B” pin B11
(raw, un-corrected pulse)

┌──────────┐
│ TL ECU │
│ │
│ B11: raw│
└─┬────────┘
│
│ internal ECU processing
▼
┌──────────┐
│ TL ECU │
│ B9: │───┬──► Yellow-Box INPUT
│ BLU/BLK │ │ (calibrator IN)
└──────────┘ │
│
┌───────────────────┴───────────────────┐
│ │
▼ ▼
Yellow-Box OUT (untouched) factory
(corrected pulse) BLU/BLK harness
│ │
└─────────┬─────────────────────────────┘
▼
MICU
│
multiplex bus
▼
Cluster
Step-by-step hookup:
Raw sensor → TL ECU

Green/White wire from the trans → ECU connector B pin 11.

Don’t touch this line—it must stay raw so the TL ECU’s logic (VTEC, knock, gear detection) remains correct.

TL ECU B9 → Yellow-Box input

On the TL-ECU adapter harness, locate pin B9 (blue/black wire).

Splice that BLU/BLK into your Yellow-Box INPUT lead.

Yellow-Box output → Accord BLU/BLK harness

Find the Accord’s blue/black VSS lead (pin 6 of the radio plug, or the same wire that runs back into the MICU).

Tap your Yellow-Box OUTPUT into that wire—do not cut the factory harness; just parallel it.

Result

TL ECU still sees raw G/W at B11, so ECU functions unaffected.

Yellow-Box takes the ECU’s analog VSS OUT (B9), corrects it, and then drives the Blue/Black line to MICU/cluster.

MICU/cluster now get your adjusted pulse and display the speed you’ve dialed in.

In essence the TL ECU (pin B9) is the source of the VSS pulse that your Yellow-Box will correct, and the corrected output feeds the MICU over the BLU/BLK harness exactly where the cluster “expects” its analog speed signal.

[keltalon]

In your 2003 Accord with the stock ECU, there is no dedicated analog “speedometer wire” carried back to the cluster—instead it works like this:

VSS Sensor → ECU
The green/white wire from the transmission sensor feeds the ECU (pin B11) with raw pulses.

ECU → Multiplex Bus → MICU → Cluster
The ECU converts those pulses into digital speed data and sends it over the multiplex network (a two-wire “bus”) to the MICU, which in turn relays it (still digitally) to the gauge cluster.

So:
TL ECU pin B9 (blue/black) is not used at all in the stock Accord harness—there’s nothing on the other end of a BLU/BLK wire going back to the ECU in the factory car.

Yet your speedometer works, because it isn’t looking for an analog pulse on BLU/BLK—it’s reading the ECU’s speed data digitally via the MICU.

What this means for your tap:
Before tapping B9 → BLU/BLK:

BLU/BLK in the Accord radio/MICU harness floats (or only feeds an accessory radio/navi if you have one)—it’s not what the cluster uses.

After tapping B9 → BLU/BLK:

You’re feeding the MICU an analog VSS pulse on its BLU/BLK input, which the MICU then converts into the same multiplexed data the cluster already uses.

You’re not “stealing” any signal that the cluster was already using—you’re simply providing the MICU with the analog feed it never had in the stock Accord.

Bottom Line
Current speed signal → fully digital on the multiplex bus between ECU, MICU, and cluster.

BLU/BLK wire → currently unused by the cluster; tapping it with B9 simply gives the MICU its analog VSS input so everything downstream (including your speedo) stays happy, now driven by the TL ECU’s B9 output.